300 PALEONTOLOGY OF NEW-YORK. 



Phityostuiiia veiitricosa. 



Platk LV. Fio. 9 a, b, c, d. 



PMyotUnaa venlricota : Conkad, Jour. Acad. Nat. Sciences of Philadelphia, 1842, Yol.viii, pa. 275, 



pi. 17, f. 5. 



•' Globose : whorls somewhat scalariform, or flattened above ; lower part 

 " of columella prominent ; labrum reflected ; width and length of 

 " aperture nearly equal." 



The specimens before me vary from globose to depressed-globose, and obliquely 

 ovoid; due perhaps in part to the original form of the shell, and more to the sub- 

 sequent accidental causes. After comparing a large number of specimens, I do not 

 find any constant or satisfactory character for the reliable separation of those occur- 

 ring in the Oriskany sandstone, from those in the Lower Helderberg group, which 

 seem to me referable to this species of Mr. Conrad. 



The Platyostoma arenosa of Conrad ( Trans. Acad. Nat. Sciences of Philadelphia, 

 Vol. viii, pa. 276, pi. 17, f . 6 ) appears to me to be only the young of P. ventricosa. 

 Some of the specimens from the Oriskany sandstone, of the same dimensions as the 

 figure cited, do not difiFer from that one; while there are numerous intermediate 

 forms, which, in the casts, cannot be satisfactorily distinguished. 



As this fossil appears in its various forms, it may be described as Globose, more 

 or less depressed or obliquely subovoid : spire moderately elevated, consisting of 

 three or four volutions, the last one of which is extremely ventricose ; volutions 

 flattened upon the upper side; aperture circular or subovate; columellar lip re- 

 flexed. Surface marked by fine closely arranged strise. 



Fig. 9 a. View of a depressed-globose specimen, from which the shell is nearly removed. 



Fig. 9 6. View of the aperture of the same. [ This figure is not properly given.] 



Fig. 9 c. A globose specimen which preserves a fragment of the shell. 



Fig. 9 (f . A worn specimen, showing a longitudinal section of the shell on one side of the 

 centre. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 

 group : Catskill, and Becraft's mountain. 



